20,096 research outputs found
Co-Clustering Network-Constrained Trajectory Data
Recently, clustering moving object trajectories kept gaining interest from
both the data mining and machine learning communities. This problem, however,
was studied mainly and extensively in the setting where moving objects can move
freely on the euclidean space. In this paper, we study the problem of
clustering trajectories of vehicles whose movement is restricted by the
underlying road network. We model relations between these trajectories and road
segments as a bipartite graph and we try to cluster its vertices. We
demonstrate our approaches on synthetic data and show how it could be useful in
inferring knowledge about the flow dynamics and the behavior of the drivers
using the road network
Can a galaxy redshift survey measure dark energy clustering?
(abridged) A wide-field galaxy redshift survey allows one to probe galaxy
clustering at largest spatial scales, which carries an invaluable information
on horizon-scale physics complementarily to the cosmic microwave background
(CMB). Assuming the planned survey consisting of z~1 and z~3 surveys with areas
of 2000 and 300 square degrees, respectively, we study the prospects for
probing dark energy clustering from the measured galaxy power spectrum,
assuming the dynamical properties of dark energy are specified in terms of the
equation of state and the effective sound speed c_e in the context of an
adiabatic cold dark matter dominated model. The dark energy clustering adds a
power to the galaxy power spectrum amplitude at spatial scales greater than the
sound horizon, and the enhancement is sensitive to redshift evolution of the
net dark energy density, i.e. the equation of state. We find that the galaxy
survey, when combined with Planck, can distinguish dark energy clustering from
a smooth dark energy model such as the quintessence model (c_e=1), when
c_e<0.04 (0.02) in the case of the constant equation of state w_0=-0.9 (-0.95).
An ultimate full-sky survey of z~1 galaxies allows the detection when c_e<0.08
(0.04) for w_0=0.9 (-0.95). We also investigate a degeneracy between the dark
energy clustering and the non-relativistic neutrinos implied from the neutrino
oscillation experiments, because the two effects both induce a scale-dependent
modification in the galaxy power spectrum shape at largest spatial scales
accessible from the galaxy survey. It is shown that a wider redshift coverage
can efficiently separate the two effects by utilizing the different redshift
dependences, where dark energy clustering is apparent only at low redshifts
z<1.Comment: 14 pages, 7 figures; minor changes to match the published versio
HerMES: deep galaxy number counts from a P(D) fluctuation analysis of SPIRE Science Demonstration Phase observations
Dusty, star-forming galaxies contribute to a bright, currently unresolved cosmic far-infrared background. Deep Herschel-Spectral and Photometric Imaging Receiver (SPIRE) images designed to detect and characterize the galaxies that comprise this background are highly confused, such that the bulk lies below the classical confusion limit. We analyse three fields from the Herschel Multi-tiered Extragalactic Survey (HerMES) programme in all three SPIRE bands (250, 350 and 500 μm); parametrized galaxy number count models are derived to a depth of ~2 mJy beam^(−1), approximately four times the depth of previous analyses at these wavelengths, using a probability of deflection [P(D)] approach for comparison to theoretical number count models. Our fits account for 64, 60 and 43 per cent of the far-infrared background in the three bands. The number counts are consistent with those based on individually detected SPIRE sources, but generally inconsistent with most galaxy number count models, which generically overpredict the number of bright galaxies and are not as steep as the P(D)-derived number counts. Clear evidence is found for a break in the slope of the differential number counts at low flux densities. Systematic effects in the P(D) analysis are explored. We find that the effects of clustering have a small impact on the data, and the largest identified systematic error arises from uncertainties in the SPIRE beam
Full-Duplex Cloud Radio Access Network: Stochastic Design and Analysis
Full-duplex (FD) has emerged as a disruptive communications paradigm for
enhancing the achievable spectral efficiency (SE), thanks to the recent major
breakthroughs in self-interference (SI) mitigation. The FD versus half-duplex
(HD) SE gain, in cellular networks, is however largely limited by the
mutual-interference (MI) between the downlink (DL) and the uplink (UL). A
potential remedy for tackling the MI bottleneck is through cooperative
communications. This paper provides a stochastic design and analysis of FD
enabled cloud radio access network (C-RAN) under the Poisson point process
(PPP)-based abstraction model of multi-antenna radio units (RUs) and user
equipments (UEs). We consider different disjoint and user-centric approaches
towards the formation of finite clusters in the C-RAN. Contrary to most
existing studies, we explicitly take into consideration non-isotropic fading
channel conditions and finite-capacity fronthaul links. Accordingly,
upper-bound expressions for the C-RAN DL and UL SEs, involving the statistics
of all intended and interfering signals, are derived. The performance of the FD
C-RAN is investigated through the proposed theoretical framework and
Monte-Carlo (MC) simulations. The results indicate that significant FD versus
HD C-RAN SE gains can be achieved, particularly in the presence of
sufficient-capacity fronthaul links and advanced interference cancellation
capabilities
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